This study examines the impact of cognitive load (CL) on lower limb biomechanics during the take-off preparation phase of the platform serve in tennis players of varying skill levels. Fifteen elite and fifteen amateur tennis players performed platform serves before and after completing a 30-minute Stroop task designed to induce CL. Key biomechanical parameters, including joint range of motion (ROM), joint moments, centre of mass (COM) displacement, and ground reaction force (GRF), were assessed using both kinematic and kinetic analysis. After CL, the biomechanical performance of amateur athletes significantly decreased compared to elite athletes. Specifically, amateur athletes showed a 14.19° lower ankle joint range of motion in the sagittal plane (p < 0.001), a 0.04-meter lower COM displacement in the frontal plane (p = 0.017), and a 0.15 Nm/BW lower knee extension moment (p < 0.001). CL adversely affects the lower limb biomechanics of amateur players more than elite players, with elite players demonstrating greater stability. These findings suggest that elite players have developed more efficient motor control mechanisms through extensive training. Tailored training interventions that account for different skill levels could enhance performance stability and mitigate the risk of injury.

The quantum boomerang effect is a counterintuitive phenomenon in which a wave packet launched with finite momentum in a disordered medium returns to its origin. However, up to now, the experimental exploration of this boomerang effect remains largely unexplored. Here, we report the observation of this effect with light in an on-chip, one-dimensional (1D) disordered waveguide lattice. After benchmarking the system through Anderson localization, we launch a kinetic light beam into the system and track its center of mass (COM): it first moves away from its starting point, arrives at a maximum-valued point, reverses its direction, and returns to its original position over time, revealing the real-space observation of the photonic quantum boomerang effect. We also show two methods to accelerate and control the return: a symmetric gradient loss and time-varying coupling control to effectively increase the return velocity. Both strategies are realized experimentally and captured by our model. These results establish a controllable photonic platform for boomerang physics and open an avenue for future study in nonlinear and many-photon regimes.

Individuals with incomplete spinal cord injury (iSCI) often fall due to decreased sensorimotor integration. Functional electrical stimulation (FES) therapy combined with visual feedback balance training (VFBT), termed FES+VFBT, can effectively improve standing balance in iSCI populations. Although promising, the need for force plates (FP), which are expensive and bulky, limits the translation of these methods to clinical and home settings. In this work, we propose a solution by replacing FP with Wii Balance Board (WBB), allowing for more accessible FES+VFBT at a lower cost in both clinical and community settings. Our investigations on ten non-injured participants reveal that WBB-based estimated center of mass (COM) has low prediction error and high correlation in both anteroposterior (RMSE: 4.13 ± 0.69 mm, r: 0.94 ± 0.02) and mediolateral directions (RMSE: 6.25 ± 1.80 mm, r: 0.92 ± 0.04) with ground FP-estimated COM, resulting in similar stimulation patterns obtained with the WBB-based approach, indicating that the WBB-based FES+VFBT system could yield a more accessible therapeutic strategy for balance rehabilitation in iSCI.

The center of mass is a key parameter characterizing the mass distribution of an object, and its measurement holds significant importance in high-tech fields such as aerospace, the defense industry, and precision manufacturing. With modern engineering demanding ever-increasing spacecraft flight stability, control precision, and precision measurement requirements, the accuracy, efficiency, and adaptability of center of mass measurement have also become research hotspots. This paper systematically reviews current mainstream measurement techniques, including static and dynamic methods, while analyzing their respective advantages and sources of error. By comparing Chinese and non-Chinese achievements in center of mass measurement equipment development and engineering applications, it identifies existing challenges and issues in the field and outlines future trends in center of mass measurement technology.

Low-energy electron attachment to molecules often leads to the formation of shape resonances, which play a pivotal role in electron-driven chemical processes. While the total decay width of a resonance determines its auto-detachment lifetime, decomposing this width into partial contributions from various auto-detachment continuum channels may provide a deeper insight into the underlying decay dynamics. In this work, we explore the applicability of using bound state methods, in particular the analytic-continuation based stabilization method, for determining partial widths in medium-sized organic molecules. Angular momentum-resolved partial widths can be obtained by placing diffuse functions at the molecular center of mass. Using the stabilization method combined with the equation-of-motion electron attachment coupled cluster method, we applied this technique to pyridine and uracil, two prototypical π-conjugated systems, and analyzed the contributions of s-, p-, d-, f-, g-, h-, and i-type functions to the widths of shape resonances. Our results show that the dominant angular momentum component of each resonance width correlates strongly with the nodal structure of the corresponding resonant orbital. Importantly, we find that higher angular momentum functions, particularly d, f, g, and h, play a decisive role in accurately capturing resonance widths. Compared to conventional atom-centered augmentation schemes, the center of mass-based approach alleviates some of the uncertainties in the stabilization method associated with inconsistent avoided crossings.

ABSTRACT In the absence of any rational framework in the seismic standards, shifting of the floor centre of mass (CM) on either side to account for the accidental torsion in time history analysis has now become a standard practice. Shifting of CM leads to the alteration of eigen properties of the building, thereby resulting in an interesting paradox: increasing the accidental eccentricity may also lead to an underestimation of design member force resultants. This paper aims to quantify the accidental eccentricity contributed by torsional ground motion when using the response history analysis. A wide range of one‐storey torsionally coupled buildings subject to a suite of seismic events comprising the recorded orthogonal pair of horizontal accelerograms and the recorded torsional accelerogram are considered. The proposal for accounting for the torsional ground motion in response history analysis is to derive an artificial torsional component from the scaling of the recorded horizontal pair through a function of accidental eccentricity. Accidental eccentricity required, in a median sense, to account for the torsional ground motion, arguably the most dominant contributor of accidental torsion, is first evaluated considering the directionality effect of a horizontal pair of seismic excitations. Recommendations for accidental eccentricity are then proposed that are contingent on a pair of system parameters: the uncoupled torsional period and radius of gyration. Implementation of the proposed accidental eccentricity to a multistorey building is also illustrated. The example problem considered here shows that the proposed accidental eccentricity successfully captures displacement and drift demands at all floor levels.

BackgroundForward propulsion during walking is generated by different joints and biomechanical mechanisms depending on environmental and task demands. Although propulsion can be modulated by feedback, it is unclear whether extrinsic and intrinsic feedback generate similar propulsion or promote different joint-level strategies during split-belt walking. The purpose of this study was to investigate strategies used by non-impaired individuals to generate greater propulsion using different feedback to reach targeted levels of propulsion force during split-belt walking.MethodsFifteen young adults walked on a split-belt treadmill with the dominant leg on the fast belt at their comfortable walking speed and the non-dominant leg on the slow belt at half speed. They performed trials with extrinsic via visual feedback of propulsive force (targeting 5 and 10% body weight) and with intrinsic feedback via a backward resistive force at the center of mass (5 and 10% body weight). Primary outcome was propulsion accuracy, measured as average propulsion error relative to target levels. Secondary analyses examined explanatory biomechanical variables related to propulsion generation. Outcomes were analyzed using two-way repeated measures ANOVA with Bonferroni correction.ResultsParticipants achieved similar target propulsion across feedback types (p = 0.66). However, biomechanical strategies differed. Visual feedback increased trailing limb angle (TLA) at 5% (p = 0.0011) and 10% (p < 0.0001) and increased ankle moment at 5% (p = 0.0005) and 10% (p < 0.0001). In contrast, backward resistive force increased (BRF) hip moment at 5% (p = 0.0018) and 10% (p < 0.0001), and hip power at both 5 and 10% (p < 0.0001). Ankle power did not differ between feedback types at 5% (p = 0.0754) but was greater under BRF at 10% (p < 0.0001).ConclusionWhile both feedback types generate similar propulsion to achieve different target levels during split-belt treadmill walking, they engaged distinct biomechanical strategies. Our results indicate that participants increased TLA and ankle moment under visual feedback. However, they increased hip moment and hip power under BRF, with ankle power adjustments depending on the target level. The findings highlight motor abundance in gait and suggest tailoring rehabilitation strategies in populations with impaired propulsion.

To investigate the contribution of knee adduction moment (KAM) lever arm components and examine their relationships with gait variables in Early-mild and Severe osteoarthritis (OA) groups. Female patients with medial knee OA were classified into two groups: Early-mild (Kellgren-Lawrence (KL) grade 1-2, n = 46) and Severe (KL 3-4, n = 40). At the first peak of KAM, we measured the lever arm; the lateral positions of the body center of mass, knee joint center, and foot center of pressure (foot COP); and the frontal plane angles of the trunk, pelvis, hip, and knee. Additionally, foot progression angle and step width were measured. Hierarchical multiple regression determined the contribution of lever arm components, and partial correlation assessed their relationships with gait variables. In both groups, smaller knee varus angle (Early-mild: β = 0.563; Severe: β = 0.346) and more lateral foot COP position (Early-mild: β = - 0.316; Severe: β = - 0.686) were associated with a shorter lever arm. Knee varus angle and foot COP explained 46.4% and 4.8% of lever arm variance in Early-mild group, and 11.3% and 35.6% in Severe group. Smaller contralateral pelvic drop and greater hip adduction related to smaller knee varus angle. Especially in Early-mild OA, greater toe-in was associated with smaller knee varus. Additionally, greater toe-in and wider step width were related to foot COP closer to the knee. The characteristics of the contributions of the lever arm components and related gait variables were revealed in Early-mild and Severe OA. These findings may inform gait strategies to reduce KAM.

The structural dependence of self-propelled motion in micro/nanomotors is essential for effectively predicting and controlling their dynamic behaviors. In this study, platinum–silica (Pt-SiO2) micromotors, with structures ranging from spherical Janus to dimer configurations, are fabricated through conventional template-assisted deposition, followed by annealing. These structures are used to investigate how geometry influences motion. Our results demonstrate that the architecture of the Pt-SiO2 micromotor strongly affects its propulsion mode and trajectory in solution. When immersed in a hydrogen peroxide (H2O2) solution, spherical Janus Pt-SiO2 micromotors exhibit quasi-linear motion, driven by the Pt side (Pt pushing). In contrast, dimeric structures and intermediate forms varied from Janus to dimer display quasi-circular trajectories with continuously changing directions, characteristic of Pt-dragging motion. We reveal that these distinct propulsion behaviors stem from differences in the spatial distribution of Pt on the SiO2 sphere surface. Variations in Pt distribution alter the exposed silica surface area—rich in hydroxyl groups—which modulates the driving force and causes the resultant force acting on the micromotor to deviate from its mass center axis (or the axis connecting the mass centers of the Pt component and silica sphere), thereby inducing circular motion. This study offers a versatile strategy for fabricating Pt-SiO2 micromotors with tailored structures and advances the fundamental understanding of structure-dependent self-propulsion mechanisms.

Ikeda, Y, Kawabe, M, and Hisamitsu, T. Influence of lower-extremity joint torque and power during vertical and horizontal jumps on swimming start performance in competitive swimming. J Strength Cond Res 40(1): e50-e61, 2026-Jumping ability plays a crucial role in optimizing kick start performance in swimming. However, effective training methods for transferring the enhanced jumping ability to the kick start movement remain unclear owing to insufficient understanding of the relationship between kick start and jump movements. This study explores the relationship between kinematic parameters during the kick start and leg muscular power output in horizontal and vertical jumps. Fourteen male competitive swimmers (20.2 ± 2.3 years) participated in the swim start and jump tests. Jump performance was evaluated using vertical jumps (VJ), squat jumps (SJ), and standing long jumps (SLJ). Key metrics included the jump height (VJ, SJ), horizontal distance (SLJ), take-off velocity, joint torques, and power output. The results showed that flight distance, influenced by the vertical velocity of the center of mass (CM) at take-off, was significantly correlated with 5-m and 10-m performance (P < 0.05). Jump performance metrics were notably associated with swim start parameters, highlighting the importance of jump direction. However, these metrics did not correspond to the vertical velocity of the CM at take-off during the kick start (r = -0.059-0.473, n.s). Swimmers with greater flight distances exhibited higher joint torques and power in the knee and ankle joints during jumps, as along with greater deviation of the CM take-off angle during the kick start. These findings suggest distinct technical requirements for enhancing both flight distance and CM horizontal velocity. Targeted resistance and plyometric training, combined with technical adjustments in CM positioning, may improve swimming start performance.

We present a comparative analysis of methodologies for studies of wetting behavior of liquid nano-droplets. Different droplet sizes were simulated using molecular dynamics (MD) under both complete and partial wetting conditions. The results show why conventional root mean square displacement (RMSD) metrics are inadequate for capturing finite system dynamics based on internal, center of mass, and coupling contributions to its value. The z-component of the center of mass is proposed as an alternative, accurate descriptor. A new equation for the contact radius of nano-droplets is derived using the radius of gyration (Rg) of interfacial molecules. In addition, a modified sinc kernel smoother is employed to develop a new method for calculating the dynamic contact angle. The accuracy and robustness of both the new and conventional methods were evaluated through calculations of physical properties, including apparent line tension and contact angle. The apparent line tension is positive only in highly hydrophilic systems and negative otherwise. Young's contact angle shows consistent results across methods for hydrophilic cases but varies in hydrophobic systems, signifying its dependence on the droplet shape analysis technique. The proposed methods yield physically meaningful results and are more reliable than standard circle fitting techniques.

Increased backpack weight might lead to increased trunk stiffness during walking in primary school aged children: A pilot study.

Lumbopelvic moments are key contributors to lower limb forward acceleration and deceleration in male runners.

In order to ensure stable movement of differential drive robots on slopes, a control algorithm for stable movement of differential drive robots on slopes in non flat terrain is proposed. By planning the wheel motion conversion process that adapts to changes in terrain slope, the differential drive robot generates wheel motion sequences that are suitable for different slopes. Construct an evaluation function based on stability constraints, select a state with good motion as the next motion state of the robot, and adjust the lateral position of the robot to meet the stability margin requirements. On this basis, a deep enhancement method based on RBF neural network and Q-learning is introduced. With the change of the current environmental state value of the differential drive robot, through continuous training and learning, the network weights and wheel motion parameters are updated in real time, and the optimal execution wheel motion mode is selected to achieve stable slope movement control of the differential drive robot in non flat terrain. The experimental results show that under non flat ground conditions, the proposed algorithm has small changes in the horizontal velocity of the center of mass, the energy curve is consistent with the ideal, the stability margin is greater than 0.60 units, and the success rate of wheel motion conversion is greater than 92%; On a gentle slope, with a stability margin of 0.75, a moving speed of 1.0 m/s, a wheel motion conversion success rate of 98%, a recovery time of 2.0 seconds, and an error of 0.1 meters, the differential drive robot can achieve stable movement in non flat terrain.

In the design of rod mechanisms and robotic manipulators, one of the key challenges is ensuring their strength and stiffness. There are various approaches to solving this problem—force methods, displacement methods, lumped parameter models, and the finite element method (FEM). The FEM approach divides the model into individual finite elements and relates the displacements at the nodes to the acting forces using a global stiffness matrix. However, all these calculation methods do not take into account the distributed inertial loads that arise from the mass of the links during motion, as well as the gravitational forces that result from this mass distribution. The distribution of mass and inertia is critically important, since the mass of a rod-like link is a distributed parameter along its length. Traditionally, in dynamic simulations and strength analyses, inertia is considered by applying resultant force vectors and moments of inertia at the center of mass of each link. This approach is generally incorrect, because inertial forces—like gravitational forces—are inherently distributed. A review of scientific publications on this issue shows that none of the above-mentioned methods account for the distributed inertia of planar motion in rod mechanisms and robotic manipulators when analyzing strength and stiffness. Only relatively recently, an original method was developed that considers distributed inertia in the case of purely planar motion of such structures. In this work, we propose a new approach to this calculation problem, applicable not only to planar, but also to spatial models based on FEM. The relevance of our method lies in its ability to more fully incorporate distributed inertia effects, as it allows for strength and stiffness analysis of both planar and spatial rod mechanisms (RM) and robotic manipulators (RM). In addition to the theory and algorithm, this paper presents condensed results of force and elastic displacement calculations using an example that demonstrates the application of the previously developed method.

Biped robots are distinct systems owing to their multi-degree of freedom construction, intrinsic instability, and highly nonlinear dynamics. Owing to these, gait pattern generation to ensure stable locomotion represents an important area of research for these robotic systems. The purpose of gait pattern generation for biped robot is to infuse stability in the system by giving each joint a predetermined position with respect to time. In this work, the effectiveness of two different gait patterns for bipedal walking has been investigated, compared and the results are presented. The gait patterns investigated are the one based on Rolling Sphere Model (RSM) with predefined Zero Moment Point (ZMP) as stability criteria and the gait pattern based on 3D Linear Inverted Pendulum Model (LIPM) with tracking of Capture Point (CP). As the design of Center of Mass (CoM) trajectory forms the basis of such model based gait pattern generations, the effect of CoM trajectory on the stability of biped robotic system is analyzed. The variations in other parameters such as joint positions and torques, ZMP determined with the help of contact forces of the ground, and comparative study in terms of kinetic energy and total energy is carried out and the results are presented. It is observed that the case dealing with ZMP based gait pattern offers an efficient method in terms of consumption of energy.

For the reaction 12C(γ,np) 10B, a kinematic model was developed assuming a sequential two-particle decay with the formation of an intermediate excited nucleus. The possibility of decay through two channels - (n+11C*) or (p+11B*) - was created. In the system of the center of mass of a two-particle reaction, the kinematics is determined by the fact that, regardless of the specific type of interaction, the reaction products scatter at an angle of 180 and have equal modulus momentum, and their energies in the same system depend only on the masses of the particles and the total energy of the system. To visualize model calculations in the Python programming language, a graphical application was created with the possibility to interact with experimental data on the 12C(γ,np) 10B reaction. Comparison of kinematic calculations with experimental results allowed us to identify certain limitations for the selection of experimental events corresponding to the channel of sequential two-particle decay.

In multi-objective particle swarm optimization (MOPSO), challenges persist, including low diversity in external archives, ambiguous individual optimal choice mechanisms, high sensitivity to parameter settings, and the arduous task of balancing global exploration and local exploitation capabilities. To address these issues, this paper introduces a novel multi-objective particle swarm optimization algorithm named HCRMOPSO. The proposed algorithm innovatively leverages hierarchical clustering based on Ward’s linkage to generate the center of mass as reference points, which are then combined with the ideal point and crowding distance. This effectively maintains the external archive, thereby resolving the diversity deficiency commonly found in traditional MOPSO archives. Additionally, HCRMOPSO fuses multiple particles to update the personal best positions. It also adaptively tunes the flight parameters according to the diversity information within each particle’s neighborhood, enhancing the algorithm’s adaptability. Notably, a new strategy is designed for two specific types of particles, further optimizing the search process. The performance of HCRMOPSO is rigorously evaluated against ten existing algorithms on 22 standard test problems. Experimental results demonstrate that HCRMOPSO outperforms its counterparts on multiple benchmarks, showcasing superior effectiveness in handling multi-objective optimization tasks.

Plant oil-based elastomer has advantages such as sustainability, environmental friendliness, good biocompatibility, and high stretchability. However, the multiscale mechanical mechanisms of these materials remain unclear, limiting further optimization and application. This study focuses on palm oil-based elastomers, which feature hydrogen bond-toughened branched polymers. The effect of carboxyl modification of carbon-carbon double bonds in fatty acid chains on the mechanical behaviors of molecular segments (1-10 Å), single polymer molecules (1-10 nm), and polymer aggreagates (10-100 nm) was investigated using molecular dynamics simulations. Carboxyl modification significantly enhances the flexibility of molecular segments. As the number of carboxyl groups on a linoleic acid chain increases from 0 to 2, the average end-to-end distance reduces by 29% and the standard deviation increases from 0.23 to 6.6 Å. At the scale of single polymer molecules, carboxyl modification leads to more compact conformations and reduced conformational variability. With the number of carboxyl groups increasing from 0 to 6, the fluctuation of the radius of gyration reduces by 42.9%. At the scale of polymer aggregates, as the carboxyl modification rate increases from 0 to 100%, hydrogen bond density rises from 1.8 to 2.8 nm-3, free volume fraction decreases from 16.8 to 14.5%, and diffusion coefficient drops from 6.7 × 10-4 to 3.3 × 10-4 Å2/ps. Simultaneously, the strengthened intermolecular interactions induce stretching and expansion of the polymer chains. Hydrogen bonds are mainly formed between the hydrogen and oxygen atoms on the polymer backbone. The maximum tensile stress increases from 0.23 to 0.26 GPa and the stress at a strain of 120% increases by 58%. The greater changes in relative positioning of polymer mass centers indicate a significant role of viscous deformation after carboxyl modification. Correlation analysis reveals that increased carboxyl modification enhances chain flexibility at the molecular segment scale, improves conformational compactness and stability at the single polymer-molecule scale, and strengthens the mechanical performance at the polymer aggregate scale. This study provides insights into the multiscale mechanisms of hydrogen bond-toughened palm oil-based elastomer and offers the basis for the design and optimization of plant oil-based materials.

Active space debris removal operations require a priori knowledge of the target objects’ rotation parameters, i.e., information on their rotation speed and current orientation in space. This can be achieved through appropriate observations designed to determine these parameters. Recording and subsequent analysis of light curves is the most common method for monitoring space objects’ rotation using optical means. This paper examines the results of long-term photometric observations of a large space debris object — the third stage of the SL-14 rocket (international COSPAR number 1987-074G, USSTRATCOM ID 18340). It shows how this resident space object’s (RSO) rotation speed around its center of mass repeatedly changed between 2006 and 2025. To understand the cause of this behavior of RSO 18340, it is necessary to study the relationship between its different rotation speed states and the corresponding orientation of its rotation axis in inertial space. In paper, we consider the observed light curves of RSO 18340, recorded in 2024 at different observatories, analyze their structure and identify similar photometric patterns in different light curves. These photometric patterns are used to determine the spatial direction of the object’s rotation axis in two short (1–3 days) time intervals in late February – early March 2024. As a result of this analysis of the light curves, four estimates of the average direction of the rotation axis and its evolution over a two-week interval were obtained. Using two light curves obtained during flybys over different observing points on February 27, 2024, we obtained the current direction of the rotation axis in the inertial coordinate system: RA = 10°, Decl. = -66°. And based on six light curves obtained on March 9, 10 and 11, 2024, the following average coordinates were determined: RA = 06°, Decl. = -39°. We estimate the internal error of these results to be ±(5–10)°. Based on these results, we hypothesize that there are no rapid shifts in the rotation axis of RSO 18340.